Such ventilation devices are, for example, also known from EP 1 924 772 B1, GB 1 256 625, DE 30 10 071 A1 and DE 32 41 860 C3. Such ventilation devices are used as so-called air handling units (AHUs) for air treatment, for example, to heat, cool and/or humidify air in residential buildings. They consist of, among other things, a fan which blows or suctions air through the filter, the heat exchanger and/or the heating coil. Such units suction air from one or several ducts that are connected to different rooms in a residential building and, at the outlet of the device, blow the air into a duct system which directs the treated air to different living areas. From the fluidic perspective, these known ventilation devices are characterized in that they consist of a fully closed duct through which the air is directed in the axial direction from the air inlet opening to the air outlet opening. The fan provided in the duct, consisting of the electric motor and the fan impeller, is used to overcome the pressure drops that occur in the duct system. The fan driven by the electric motor represents a substantial electrical load because it requires a considerable electrical input capacity. Furthermore, the heating, cooling and/or air humidifying units generate high flow drops. Furthermore, the known ventilation devices generate a quite significant running noise. Double flow fans with forward curved radial impellers are in particular used in the known devices. An asynchronous internal rotor motor is normally used as an electric motor. Due to their construction, the known fans in use, with forward curved blades at their fan impellers, have a relatively low degree of efficiency.